1. Field of the Invention
The present invention relates in general to an assembly for mounting the shank of a ground working tool to the tool bar of a soil tilling farm implement, and more specifically relates to an assembly that releases the ground tool for pivotal movement out of an operating position upon encountering an obstruction in the soil.
2. Description of the Prior Art
Assemblies for movably mounting ground tools to a tool bar of a soil tilling farm implement are well known in the art. A typical such assembly is disclosed in U.S. Pat. No. 2,493,811, wherein a tool has a shank pivotally interconnected to a support plate and to a spring unit that has a coil spring compressed when the tool is pvioted. The coil spring provides an initial pressure on the tool to hold it in a normal operating position during a soil tilling operation. When the tool encounters an obstruction in the soil, the force applied on the tool overcomes the initial spring pressure, compresses the coil spring and pivots the tool from the normal operating position therefor. When the obstruction has been passed, the compressed spring causes the tool to return to its normal operating position.
The above type of tool mounting assembly provides an improvement over a fixed mounting of a tool on a tool bar. However, in operation the pressure exerted by the coil spring, during pivotal movement of the tool to the obstruction passing position therefor, is progressively increased. U.S. Pat. No. 3,700,039 discloses an assembly intended to reduce this problem by decreasing the moment arm of the spring force, as the spring is compressed, so that the counter force required to pivot the tool from an operating position is maintained only slightly greater than the initial force acting to hold the tool in the operating position. However, neither of the above references discloses an assembly that holds the tool in an operating position with a force that is substantially negated as the tool is pivoted out of the operating position whereby to minimize tool damage that may result from encountering an obstruction.